Specify CVXPY version to use '*' for matrix multiplication

[rahulnair23]

pip install pulls the latest version of CVXPY, version 1.1.15. Using the the BRCG algorithm with this version results in the following run time warning several times that cannot be filtered.

UserWarning: This use of ``*`` has resulted in matrix multiplication.
Using ``*`` for matrix multiplication has been deprecated since CVXPY 1.1.
    Use ``*`` for matrix-scalar and vector-scalar multiplication.
    Use ``@`` for matrix-matrix and matrix-vector multiplication.
    Use ``multiply`` for elementwise multiplication.

Reverting to an older version, by specifying a version in setup.py allows for this deprecated use. Assumes CVXPY isn't used by other algorithms in the toolkit.

[vijay-arya]

Thanks @rahulnair23